The characteristic observation in spondylolisthesis includes anterior collapse of disc space. Therefore, it is generally an indication for spinal fusion in an extended position, through the restoration of disc height and vertebral slip.
ALIF is one of the reasonable surgical methods for this pathology [11
]. Dennis et al. [23
] investigated the disc height after ALIF using autogeneous, cadaver, or mixed iliac crest grafts. They found that 46% of levels were actually narrower than their preoperative heights. Kumar et al. [24
] also investigated the subsequent behavior of the disc height after ALIF with femoral strut allograft. Disc height was maintained only in 59% of cases. The disc degeneration in spondylolisthesis is considered to be more severe than that in any other disc pathology, such as herniation, spondylolysis, and so on.
We compared the clinical results of ALIF for spondylolisthesis and for isthmic spondylolisthesis, which we had previously reported (). The long-term follow-up result of ALIF for spondylolisthesis was worse, and the rate of adjacent disc degeneration was high. Moreover, we performed repeated surgery for adjacent disc degeneration in 6 cases (30%) of this series (present study). One of the reasons for this is the older age population. These patients had severe multi-level disc degeneration and ligament hypertrophy before the initial surgery. Therefore, decompressive laminectomy combined with some type of spinal fusion seems to be beneficial for the treatment of degenerative spondylolisthesis. However, an additional fusion surgery is not always required in case of degenerative spondylolisthesis without symptomatic instability.
Comparison of the surgical results of ALIF between spondylolisthesis and spondylolysis
Most patients presented with lower leg symptoms, such as radicular leg pain, numbness, or intermittent claudication. In case of spinal stenosis associated with spondylolisthesis (Meyerding type I) [25
], we performed decompressive surgery alone [20
]. Several authors have advised that fusion surgery should be performed only as a second stage procedure whenever necessary [3
]. The indications for ALIF are controversial: our indications for ALIF were Meyerding type II or more, and Meyerding type I with instability (symptomatic and dynamic). Symptomatic instability means severe low back pain or stiffness induced by body motion or manual labor. Most of the patients experience morning stiffness in the low back, or apprehension, frequently. Dynamic instability indicates an abnormal range of motion or translation on the lateral flexion-extension radiographs. Panjabi and White [26
] stated that translation of 10 degrees or more at L4-5, or 15 degrees or more at L5-S1 indicated radiological instability. Moreover, abnormal translation of about 2 mm or more is detectable on the plain radiographs. Johnsson et al. [27
] stated that pre- and postoperative olisthesis of less than 2 mm should not be counted. According to their criteria, we assessed the dynamic instability on the plain radiograph. We have performed ALIF in cases with these pathologies [11
In the treatment of degenerative spondylolisthesis with symptomatic or dynamic instability, fusion surgery including ALIF is necessary and important. Takahashi [10
] reported that the patients generally maintained satisfactory results up to 65 years of age. To date, the problem of the adjacent disc degeneration after spinal fusion has been pointed out [28,29
]. Biomechanical data suggested that the mobility and the intradiscal pressure of the adjacent discs were increased after single-level fusion [8
]. Clinically, adjacent disc degeneration has been implicated as a cause of low back pain. Rahm and Hall [29
] reported that adjacent disc degeneration occurred in 35% of patients and was associated with worsening of clinical results with time. But, Seitsalo et al. [30
] showed that spinal fusion did not significantly increase the rate of adjacent disc degeneration after a mean period of 13.8 years. They found no correlation between the number of degenerated discs or the degree of degeneration and subjective low back pain symptoms. It is important to clarify the cause of recurrent low back pain after ALIF, in order to improve the long-term clinical results.
In our study, the rate of bone union in the grafted area was 100%. The union rate was superior to the rate reported in the best results of a previous Japanese study [9
]. Now, the main problem was that of the adjacent disc degeneration. We found different progressive patterns of the disc degeneration according to the levels (upper or lower). The initial stage of disc degeneration was DSN. However after that, the progressive pattern of disc degeneration was different according to the adjacent levels (upper level or lower level). At the upper level, the intervertebral disc showed SIT, but the lower discs showed osteophyte formation, and occasionally lead to CSU (). Salvage surgeries were performed more frequently at the upper level than at the lower level at an average of 11.7 years after the initial operation (). Therefore clinically, the upper level is important because upper adjacent disc degeneration leads to the symptomatic disorders, which often require repeated surgery during the long-term follow-up.
Although ALIF provided satisfactory overall clinical results in the mid-term, the frequency of salvage surgeries was gradually increased due to the adjacent disc degeneration. A key decision of whether to prevent the adjacent disc degeneration during a long-term follow-up needs to be made.